This Week in Science

Science  24 Dec 2004:
Vol. 306, Issue 5705, pp. 2160
  1. Diversity with Less Competition


    Species diversity has recovered from some mass extinctions rapidly, within 1 million years or so. However, mass extinctions may also greatly effect ecosystems by altering interactions among species, and these effects may be more long lasting and cryptic. Dietl et al. (p. 2229) examined the effects of a late Pliocene extinction (about 3 million years ago) on the feeding behavior of marine snails. In an experiment, they show that snails, when competing with other snails or facing predation themselves, attack bivalves on their shell edge. When isolated, however, they attack through the cell wall—a slower but safer feeding approach. The fossil record records many edge attacks prior to the extinction, but exclusively shell-wall feeding afterward, a pattern that continues to today. Although diversity recovered promptly, the level of competition did not.

  2. Melting Metal Monolayers

    Detailed information on the electronic properties of liquids and amorphous metals is difficult to come by because the lack of long-range order in these materials limits the usefulness of most usual experimental probes. Baumberger et al. (p. 2221, published online 25 November 2004; see the Perspective by Petroff) get around the lack of long-range order by looking at a monolayer of lead deposited on a copper substrate. As the temperature is raised through the melting point of the lead layer, the underlying order of the copper substrate provides a surrogate for the energy and momentum information lost in the liquid lead thin film and allows the changes in the electronic density of states to be followed as the metal melts.

  3. Microbial Activities of the Deep

    Although deep subterranean bacterial biota have very low metabolic rates, their metabolism is highly significant on a global scale. Submarine sediment depth-profile data from the Ocean Drilling Project have provided insight into electron acceptors for bacterial respiration, including sulfate, nitrate, and oxidized iron, as well as their metabolic end products, such as sulfide and methane. D'Hondt et al. (p. 2216; see the Perspective by DeLong) used these data to estimate microbial activities deep in the sediments. The expected stratifications were upset by intrusions of oxidized compounds, such as nitrate and sulfate from the basaltic aquifer.

  4. Seek, Sense, and Destroy


    Highly virulent enterococcal strains possess a pathogenicity island within their genome that encodes, among other traits, a cytolytic toxin that uses a quorum-sensing mechanism to affect autoinduction. Coburn et al. (p. 2270; see the Perspective by Garsin) show that the bacterium actively secretes two components, an autoinducer and an anti-autoinducer. In the absence of target cells, these two interact and prevent the autoinducer from feeding back to induce high-level expression of the cytolysin. In the presence of the target cell, however, the anti-autoinducer binds to the target cell and allows the autoinducer to accumulate to the threshold level required for quorum induction of the cytolysin operon. The anti-autoinducer is itself a toxin component and effectively tags the target for destruction.

  5. Organics on Jovian Orbiters

    Amalthea and Thebe are small and irregularly shaped satellites of Jupiter that orbit very near the planet. Takato et al. (p. 2224) obtained infrared spectra of the satellites from the Subaru and Infrared Telescope Facility on Hawaii. The spectra show the presence of hydrous minerals or organic materials on the surface of Amalthea. Such materials could not have survived if the satellites formed from the circumjovian nebula, so these satellites probably are leftovers or remnants of the organic-rich building blocks from which the jovian system was formed.

  6. Complex Cell Walls

    Plant cell walls, which serve as structural support for individual plant cells and ultimately for the plant as a whole, are constructed under the direction of perhaps as many as 1000 different genes. However, these cell walls have many other functions. Analysis from a systems approach, reviewed by Somerville et al. (p. 2206), promises new insight into the complex functions of cell walls, which include regulating growth, development, responses to pathogens, and signaling.

  7. The Proteins Came in Three by Three

    Maps of protein interaction networks provide a kind of blueprint of cellular functions. Comparing the presence or absence of a pair of proteins in various species can provide clues to functional associations in such networks. Bowers et al. (p. 2246) take such logic a step further and examine the presence of groups of three proteins in 67 sequenced genomes. A search for logical relationships between the three (for example, A is present only if B and C are also present) revealed 750,000 new relationships between protein family members. These and higher-order logic relationships may be useful in modeling, engineering, and understanding biological systems.

  8. Of Migrations and Moltings

    Greater insights into the details of bird migration requires following and sampling individual birds. Using stable isotopes from feather samples, Norris et al. (p. 2249; see the cover and the Perspective by Hill) show that American redstarts migrating from Canada to the tropics adopt a strategy of molting during migration, which results in the overlap of two energetically costly activities of the annual cycle. A tradeoff was observed between molting during migration versus the timing and amount of parental care adults provide during the previous breeding season. Thus, events during a short period of the annual cycle can produce lasting effects on a migratory animal.

  9. Phosphoryl Moiety Closes the Hatch

    The calcium-dependent adenosine triphosphatase (ATPase) of the sarcoplasmic reticulum is one of the best studied ion pumps, and the structural description of two of the intermediate states in the reaction cycle helped to define the calcium ion binding sites within the transmembrane region of the enzyme. A recent series of crystal structures of the enzyme trapped at other stages in the reaction cycle is now capped by Olesen et al. (p. 2251), who identify the binding sites for the counter-transported protons. They also found that phosphoryl transfer from ATP to the enzyme closes the entry hatch to the calcium-binding site and that the release of adenosine diphosphate opens the exit hatch and allows the exchange of calcium for protons. Phosphoryl transfer from the enzyme to water and closes the exit hatch. Finally, release of phosphate opens the entry hatch and allows the exchange of protons for calcium.

  10. Hedgehog, Smoothened, and β-Arrestin


    Hedgehog (Hh) proteins carry signals that are essential for pattern formation during vertebrate embryogenesis. Extracellular Hh molecules bind to a receptor on the cell surface and activate Smoothened, a membrane-spanning protein, which transmits signals to the cell interior. β-arrestin proteins are inhibitors of G protein-coupled receptor (GPCR) signaling and also promote internalization and signaling by GPCRs. Chen et al. (p. 2257) find that in mammalian cells, activated Smoothened molecules preferentially associate with β-arrestin 2. Reducing levels of β-arrestin 2 inhibited internalization of Smoothened. Furthermore, Wilbanks et al. (p. 2264) find that loss of β-arrestin 2 in zebrafish causes developmental abnormalities similar to those of mutants in the Hh signaling pathway. Overexpression of β-arrestin 2 could partially rescue some defects in embryos with deficient Hh signaling, and loss of β-arrestin 2 decreased expression of Hh-responsive genes. Together, the findings provide insight into the roles of β-arrestin 2 during development and the mechanisms by which Hh signaling influences developmental processes from embryogenesis to cancer.

  11. Role of Transcription Factors in Neural Development

    Neural development is often thought to be a matter of axons finding the right connections. Gray et al. (p. 2255) highlight the importance of transcription in regulating neural development. Analysis of the mouse genome revealed more than 1000 genes that encode transcription factors. In situ hybridization studies further revealed that more than 300 transcription factors were differentially expressed in the central nervous system during development.

  12. Regenerating Beta Cells in Vitro

    The islets of Langerhans contain the insulin-producing β cells that must be replenished throughout life. Gershengorn et al. (p. 2261, published online 25 November 2004) show that in vitro mature β cells proliferate poorly. However, given the right circumstances, they can dedifferentiate into a mesenchymal cell type that can proliferate better but fail to produce insulin. These proliferating cells can then be induced to redifferentiate into insulin-producing β cells, which would be useful in β-cell replacement therapies for diabetes.

  13. A Human Transcriptome

    Elucidating the transcribed regions of the genome constitutes a fundamental aspect of human biology. Bertone et al. (p. 2242, published online 11 November 2004) designed and used a genome-wide high-resolution tiling array to develop a transcription map for human liver. The approach validated many known and putative genes, and in addition, more than 10,000 novel transcribed regions were identified across the genome.

  14. Potentials with All Atoms Moving

    Quantum-mechanical calculations can in principle predict the rate of any chemical reaction. In practice, however, the reaction of even a few atoms can overwhelm the most efficient computers. The problem is that when one atom moves, the range of possible motions available to every other atom in the system must be considered. Often, theorists approximate by restricting some of the atoms. In other words, they limit the potential energy surface (PES) to the one or two dimensions that seem most relevant to the reaction. Previously, the largest system for which the entire quantum-mechanical PES was considered had four atoms. Wu et al. (p. 2227) have now used an interpolation technique to consider the full 12-dimensional PES for the reaction of H atom with methane, taking into account the possible motions of all six atoms. The resulting rate constants are as accurate as the precision of reported experimental data allows, if not more so.

  15. Climate and Ecosystem Asynchrony

    The timing of climate and ecological changes recorded in land and marine records can reveal important insights into how rapidly ecosystems can—or cannot—adapt to shifts in climate (see the Perspective by Maslin). Glacial cycles are broadly controlled by the patterns of solar insolation established by Earth's orbital variations, but the exact timing of the transitions between warm and cold periods can be affected by other factors. Tzedakis et al. (p. 2231, published online 2 December 2004) compared terrestrial and marine records of climate change for the interval between 350,000 and 190,000 years ago using a marine sediment core recovered off the coast of Portugal. Abrupt changes in terrestrial ecosystems, coeval with declines in atmospheric methane, often occurred within periods that showed no such change in the marine record. This asynchrony between land and ocean records reveals that the duration of terrestrial interglacial periods cannot be fit into any particular pattern and that processes that produce millennial-scale climate variability are important determinants of the duration of warm interglacials. Both marine and terrestrial records are commonly used for climate reconstructions, and while it is fairly easy to generate precise records, establishing a common chronology for these two different types of records is much more difficult. Jennerjahn et al. (p. 2236, published online 2 December 2004) report results obtained from the analysis of marine sediment cores from the Brazilian continental margin which show that terrestrial changes can lag marine changes by 1000 to 2000 years. This time scale is much longer than that inferred for the ecological response of land plants to changes in climate found in other shorter-term studies.

  16. Constraining the Outer Core

    The outer core is composed primarily of liquid iron with about 10% by weight of a lighter element. Several elements, such as S, O, Si, and even H, have been suggested to be present, but it is uncertain how much or how many of these elements are really present in the outer core. Helffrich and Kaneshima (p. 2239) calculated the thickness of a global layer around the outer core that might be produced by liquid immiscibility in the Fe-O-S system. Then they determined, using a seismic wave that reflects within the outer core, that a layer of the appropriate thickness does not exist in the outer core. Thus, they can constrain the amount of O to less than 4% by weight and the amount of S to between 2 to 11% by weight in the outer core because such a composition would not produce an immiscible layer.

  17. Promoting and Protecting from Cell Death

    Mutations in the protein kinase Raf are frequently associated with human tumors. Raf functions in growth-promoting signaling and also acts to protect cells from apoptosis, a key event that allows cancer cells to avoid normal failsafe mechanisms that stop uncontrolled cell growth. Surprisingly, Raf's protective effect against apoptosis appears not to require enzymatic activity of Raf. O'Neill et al. (p. 2267) describe an interaction between Raf-1 and another protein kinase, MST2, in mammalian cells. Raf-1 appears to directly inhibit activation of MST2 in vitro, and this effect, like that of Raf-1 on apoptosis, was independent of catalytic activity of Raf-1. Cells lacking Raf-1 showed increased activity of MST2, which correlated with an increased propensity to undergo apoptosis. Decreased expression of MST2 protected cells from apoptosis. Thus, MST2 represents an important new target of Raf-1 that may help in the control of cell proliferation and cell death in normal and cancerous cells.